Orthogonal frequency-division multiplexing (OFDM) system is a popular digital radio communication system. Since there exists the ICI, communication reliability of the system will reduce. Therefore, many methods are used to cancel ICI for OFDM system and improve the communication reliability of the system. The existing methods for canceling ICI mainly include: frequency-domain equalization, time-domain windowing, and fixed ICI self-cancellation scheme. With reference to FIG. 1, an introduction is made in the following to the fixed ICI self-cancellation scheme, which is the closest method to the present invention.
FIG. 1 shows the structure of the relevant parts of two communication devices of the fixed ICI self-cancellation scheme, wherein the upper half part shows a transmitter of a communication device, while the lower half part shows a receiver of other communication device. Fixed ICI self-cancellation scheme implemented in the transmitter and receiver comprises the following two simple steps:
(1) at the transmitter side of the communication device, one data symbol is modulated into a group of adjacent sub-carriers with a group of weighting coefficients. For a group length of L, the optimum weighting coefficients should be designed to satisfy the polynomial P(D)=(1−D)L−1, where D denotes a subcarrier delay unit in the discrete frequency domain.
(2) at the receiver side of the other communication device, the received signals on these subcarriers frequencies are linearly combined with the proposed weighting coefficients.
By modulating a data symbol onto a group of adjacent subcarriers with predefined weighting coefficients and demodulating signals with the weighting coefficients, the fixed ICI self-cancellation scheme can have the ICI generated within a group self-cancelled each other at the receiver side. However, the function as reducing the ICI by such a repetition coding is at the cost of lowering spectrum efficiency.
The future radio communication system will be designed to combat larger frequency offset arising from higher frequency and higher mobility. In such a radio operation environment, the fixed ICI self-cancellation modulation scheme with larger group size to ensure the validity of communication must lead to lower spectrum efficiency, and the fixed modulation with comparatively higher spectrum efficiency hardly ensures the reliability of communication. It's impossible for fixed ICI self-cancellation scheme to optimize the spectrum efficiency at the prerequisite of a given performance requirement.
Therefore, there is a need for a method and a device for canceling the ICI which can not only meet the given performance requirement but also optimize the spectrum efficiency.